1. Field of the Invention
The present invention relates to a method of measuring surface properties of a polishing pad which measures surface properties such as surface topography or surface condition of a polishing pad used for polishing a substrate such as a semiconductor wafer.
2. Description of the Related Art
In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, using a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) or ceria (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad, so that the substrate is polished.
The polishing apparatus for performing the above CMP process includes a polishing table having a polishing pad, and a substrate holding device, which is referred to as a carrier or a top ring, for holding a substrate such as a semiconductor wafer. By using such a polishing apparatus, the substrate is held and pressed against the polishing pad under a predetermined pressure by the substrate holding device, thereby polishing an insulating film or a metal film on the substrate.
After one or more substrates have been polished, abrasive particles in a polishing liquid or ground-off particles of the substrate are attached to the surface of the polishing pad, and surface configuration or surface condition of the polishing pad is changed, resulting in deterioration in polishing performance. Therefore, as the substrates are repeatedly polished by the same polishing pad, a polishing rate is lowered and nonuniform polishing action is caused. Thus, dressing (conditioning) of the polishing pad is performed using a dresser to regenerate the surface configuration or surface condition of the polishing pad which has deteriorated.
In the CMP (Chemical Mechanical Polishing) process, the surface topography and condition of the polishing pad have a significant influence on the polishing performance, and thus it has been proposed to measure the surface topography and condition of the polishing pad with various measuring processes and to reflect the measured data in dressing conditions and polishing conditions.
The following documents 1 and 2 suggest that when a laser beam is applied to a surface of a polishing pad, the surface topography of the polishing pad can be measured by an optical FFT analysis of diffused reflection light from the polishing pad.
1. Takashi Kushida, Keiichi Kimura, Panart Khajornrungruang, Keisuke Suzuki “Study on evaluation method for surface topography of CMP polishing pad based on optical Fourier transform (2nd report)—Development of measuring system—”, 2012 The Japan Society for Precision Engineering Spring Meeting Academic Conference Lecture Papers, distributed Mar. 14, 2012, p. 823-824.
2. Takashi Kushida, Keiichi Kimura, Panart Khajornrungruang, Keisuke Suzuki “Study on evaluation method for surface topography of CMP polishing pad based on optical Fourier transform”, 2011 The Japan Society for Precision Engineering Autumn Meeting Academic Conference Lecture Papers, distributed Sep. 20, 2011, p. 159-160.
Further, the polishing pad and the dresser need to be replaced periodically. The time for replacement is determined based on a predetermined time period represented by a predetermined number of processed substrates or a predetermined dressing time, or an amount of wear of a polishing pad (thickness of the polishing pad). However, the predetermined time period may not necessarily become the longest usage time within the limit capable of securing the required polishing performance.